A Londoner whose debut novel has been nominated for a top literary prize against double Booker-winning author Hilary Mantel said today she is “stunned and overwhelmed” by the accolade.

Francesca Segal, 32, took American novelist Edith Wharton’s 20th-century classic The Age Of Innocence and reset it in modern-day Hampstead Garden Suburb, where she grew up.

The resulting novel, The Innocents, last night won the first novel category in the 2012 Costa Book Awards. The judges, chaired by broadcaster Dame Jenni Murray, described it as a “perfect miniature of the world it portrays” and said it was “hard to believe” this was Segal’s first effort.

The Innocents will now compete for overall Costa Book of the Year with Mantel’s Bring Up The Bodies, which won the Costa best novel category and also took the 2012 Man Booker prize. The winner will be announced on January 29.

Segal, who studied at Oxford and Harvard and is the daughter of Love Story author Erich Segal, said: “If I win, I’d think they’d made a terrible mistake. I’d have the most dreadful imposter syndrome.

“When I heard I was on the shortlist for my category I thought, ‘This is enough’. It surpasses anything I have ever dreamed of. To have won it is such an extra­ordinary feeling and I can’t even imagine winning overall.”

Segal, a freelance journalist who recently moved back to London after a stint in New York with her husband, said she started writing as a child. Her father once revealed that when she was four years old she asked him to show his publisher her work.

Segal, who lives near Gospel Oak with scientist husband Gabriel, said: “Writing is the only thing I’ve ever wanted to do. The only question was whether it was possible or practical.

“The unique gift of a first novel is you write the whole thing before anyone sees it. You have the tremendous privilege of no one watching — but with that also comes the terror.

“You are completely alone with the project and the idea it might one day have readers is the most incredibly exhilarating but terrifying concept.”

Up against Segal and Mantel are husband and wife team Mary and Bryan Talbot, who took the biography award for Dotter Of Her Father’s Eyes, poet Kathleen Jamie for The Overhaul and dyslexia campaigner Sally Gardner who triumphed in the children’s book category with Maggot Moon.